1. Field of the Invention:
This invention relates to a braking apparatus for automotive vehicles.
2. Related Art:
During a braking operation of a vehicle, a driver typically depresses a braking pedal to generate a hydraulic braking pressure that is applied to wheels of the vehicle for braking them. In an emergency case, the driver will want to stop the vehicle as quickly as possible. Therefore, the driver depresses the braking pedal strongly to generate a large braking force to be applied to the wheels.
However, as long as the braking operation is controlled by the depressing force of the driver's foot, the limited speed at which the braking pedal can be depressed will, to a certain degree limit the rate at which the strength of the braking operation can be increased. Therefore, the increase of the braking force is not satisfactorily fast. Even if an assisted braking device is provided, it merely amplifies the magnitude of a depressing force. The depressing speed itself is not increased sufficiently.
Furthermore, to stabilize a vehicle body during a braking condition, an adjustment of a braking force applied to each wheel is typically performed so as to lock front wheels early. For example, as indicated by a solid line in FIG. 20, a distribution between a front wheel braking force and a rear wheel braking force is usually designed or preset to cross a line representing a front wheel locking limit.
For this reason, there is a time lag between an initiation of an anti-skid control for front wheels and an initiation of an anti-skid control for rear wheels.
Accordingly, after the anti-skid control is started for the front wheels, a driver needs to depress a braking pedal by a significant stroke equivalent to a position Bm representing the maximum braking force for the rear wheels. Therefore, as shown in FIG. 21, a significant amount of pedal depression force is necessary. More specifically, in a section I of FIG. 21, the deceleration G is not increased regardless of an increase of the pedal depression force. Then, in a section II, the rear wheel braking force is gradually increased with increasing pedal depression force. Thus, the obtainable deceleration G is not so large.
An overly long period of time is therefore required to increase the braking force of all wheels to the maximum value. The braking performance will therefore be undesirably affected.
In other words, different behaviors of different wheels, if occuring during a braking condition, will cause a problem in braking performance. Even if all wheels are designed or preset to have similar behaviors at the beginning, such settings will be differentiated by a loading weight that flexibly varies the weight balance. In such a case, there is a possibility that a rear locking limit line may be crossed early. Therefore, setting the same behavior to all wheels from the beginning is extremely difficult.